Scientists say they are racing to discover what it is causing a massive die-off of bats in Connecticut before the condition spreads to the U.S. South.

As many as 90 percent of Connecticut's bats have died during winter hibernation after being infected by a rare fungus usually only found in Arctic tundra regions, and scientists are working to find a cause before the "white-nose syndrome" is spread to the large bat populations of the U.S. South, The Hartford (Conn.) Courant reported Sunday.

The newspaper said researchers are working on two theories. One is a study of the fungus led by the U.S. Geological Survey's National Wildlife Health Center in Madison, Wis., while the other, led by Indiana State University's Center for North American Bat Research and Conservation, is looking at the bats' diets and how they metabolize food during hibernation.

The survival of the bats is important because each one eats as many as 3,000 mosquitoes and insects every night, a control that's needed for farm and forest ecosystems, experts say.

An estimated 1 million bats have died in the northeastern United States since white-nose syndrome was first detected, the Courant said.